High speed image sensors have been widely used in many applications in different fields including the automotive field, the machine vision field, and the field of professional video photography. The technology used to manufacture image sensors, and in particular, complementary-metal-oxide-semiconductor (CMOS) image sensors, has continued to advance at great pace. For example, the demand of higher frame rates and lower power consumption has encouraged the further miniaturization and integration of these image sensors.
In addition to the frame rate and power consumption demands, image sensors are also subjected to performance demands. The quality and accuracy of the pixel readouts cannot be compromised to accommodate the increase in frame rate or power consumption.
In order to reduce the noise on the image output, current image sensors are multisampling in ramp ADC. However, the current image sensors require time, power, and chip area to perform the multisampling in ramp ADC effectively.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.